Inform user if qalc or fdfind isn't installed

[mmstick]

• If attempting to use the calc plugin without qalc installed, the search result will be a message stating that it isn't installed.
• Does the same for the find plugin with fdfind

Closes #30

[jacobgkau]

This is working for qalc. For fdfind, I'm seeing app search results if I type find without it installed, and once I type a space, the results seem to get stuck:

Screencast.from.10-06-2021.05.14.36.PM.mp4

journalctl is showing pop_launcher_plugsin::find: failed to spawn fdfind process: No such file or directory. I don't see anything like that when I get the qalc command is not installed message.

[mmstick]

It was missing a "Finished" message. Fixed.

[jacobgkau]

This PR is touching the terminal plugin, was it supposed to include 6cdf298? (Can we rebase now that #34 is merged? I was checking because I didn't want that to get undone.)

[mmstick]

I can rebase

[jacobgkau]

I'm no longer getting the freeze, but not getting any message about fdfind not being installed:

The qalc message is still working.

[mmstick]

Forgot to .await the sending of the message.

[jacobgkau]

Working now! Is there a reason we say qalc command is not installed for qalc but only fdfind is not installed for fdfind? From what I can tell, both are commands. (In Ubuntu, qalc is actually the name of the qalc package, where fdfind's package is actually fd-find.)

[mmstick]

I can fix the wording of the message.

[jacobgkau]

Looks good, both plugins are working properly and displaying the message when needed on both 21.04 and 20.04.